Alkenyl aromatic compound-conjugated diene block copolymer and process for the production thereof

Abstract

An alkenyl aromatic compound-conjugated diene block copolymer having a combined alkenyl aromatic compound content of 25-95% by weight, characterized in that said copolymer is represented by the formula, A--B--A wherein A represents an alkenyl aromatic compound polymer block, the total amount of A's in both ends being 50-97% by weight of the total combined alkenyl aromatic compound content; B represents a conjugated diene-alkenyl aromatic compound copolymer block, said B portion having (a) 2-10 taper blocks where the amount of the alkenyl aromatic compound increases gradually and (b) a weight ratio of alkenyl aromatic compound/conjugated diene of 3-85/97-15; and the total amount of the chains that 1-4 alkenyl aromatic compound monomers are linked is 5-30% by weight of the total combined alkenyl aromatic compound content. Said copolymer is excellent in the balance of impact strength, tensile strength and elongation.

What is claimed is: 
     
       1. An alkenyl aromatic compound-conjugated diene block copolymer having a combined alkenyl aromatic compound content of 25-95% by weight, wherein the block copolymer is represented by the formula;   A--B--A     wherein A represents an alkenyl aromatic compound polymer block, the total amount of said A in both ends being 50-97% by weight of the total combined alkenyl aromatic compound content, and B represents a conjugated diene-alkenyl aromatic compound copolymer block, and a homopolymer block of a conjugated diene homopolymer selected from the group consisting of polybutadiene, polyisoprene and polypiperylene, said conjugated diene-alkenyl aromatic compound copolymer block having (a) 2-10 taper blocks in which the amount of the alkenyl aromatic compound increases gradually and (b) a weight ratio of alkenyl aromatic compound/conjugated diene of 3-85/97-15, and wherein the total amount of the alkenyl aromatic compound monomers having a chain of 1-4 molecules in the polymer block is 5-30% by wt. of the total combined alkenyl aromatic compound content.   
     
     
       2. The alkenyl aromatic compound-conjugated diene block copolymer according to claim 1, wherein the weight ratio of alkenyl aromatic compound/conjugated diene in B is 5-60/95-40. 
     
     
       3. The alkenyl aromatic compound-conjugated diene block copolymer according to claim 1, wherein the total amount of A's in both ends is 70-97% by weight of the total combined alkenyl aromatic compound content. 
     
     
       4. The alkenyl aromatic compound-conjugated diene block copolymer in the form of a resin according to claim 1, wherein the combined alkenyl aromatic compound content in the copolymer is more than 55% by weight but not more than 95% by weight. 
     
     
       5. The alkenyl aromatic compound-conjugated diene block copolymer according to claim 1, wherein the B portion has 3-10 taper blocks in each of which the amount of the alkenyl aromatic compound increases gradually. 
     
     
       6. The alkenyl aromatic compound-conjugated diene block copolymer in the form of an elastomer according to claim 1, wherein the combined alkenyl aromatic compound content in the copolymer is 25-55% by weight, and the weight ratio of alkenyl aromatic compound/conjugated diene in the B portion is 3-15/97-85. 
     
     
       7. The alkenyl aromatic compound-conjugated diene block copolymer according to claim 4, wherein the total amount of the chains by which 1-4 alkenyl aromatic compound monomers are linked is 5-25% by weight of the total combined alkenyl aromatic compound content. 
     
     
       8. The alkenyl aromatic compound-conjugated diene block copolymer according to claim 4, wherein the combined alkenyl aromatic compound content in the copolymer is 60-90% by weight. 
     
     
       9. The alkenyl aromatic compound-conjugated block copolymer in the form of a resin according to claim 4, wherein the total amount of said A in both ends is 70-97% by wt. of the total combined alkenyl aromatic compound content, and the total amount of the alkenyl aromatic compound monomers having a chain of 1-4 molecules in the polymer block is 5-25% by wt. of the total combined alkenyl aromatic compound content. 
     
     
       10. The block copolymer according to claim 1, 4 or 6, wherein the weight average molecular weight of said block copolymer is 10,000-800,000. 
     
     
       11. The block copolymer according to claim 1, 4 or 6, wherein the weight average molecular weight of said block copolymer is 50,000-500,000. 
     
     
       12. The block copolymer according to claim 11, wherein the weight average molecular weight of the A portion is 3,000-150,000, and the weight average molecular weight of the B portion is 5,000-340,000. 
     
     
       13. The block copolymer according to claim 1, 4 or 6, wherein the alkenyl aromatic compound is styrene, α-methylstyrene, p-methylstyrene, m-methylstyrene, o-methylstyrene, p-tert-butylstyrene, dimethylstyrene or vinylstyrene. 
     
     
       14. The block copolymer according to claim 1, 4 or 6, wherein the alkenyl aromatic compound is styrene. 
     
     
       15. The block copolymer according to claim 1, 4 or 6, wherein the conjugated diene is butadiene, isoprene or piperylene. 
     
     
       16. The block copolymer according to claim 1, 4 or 6, wherein the conjugated diene is butadiene. 
     
     
       17. The block copolymer according to claim 14, wherein the conjugated diene is butadiene. 
     
     
       18. The alkenyl aromatic compound-conjugated diene block copolymer according to claim 1, wherein the amount of conjugated diene/alkenyl aromatic compound in each of the 2-10 taper blocks is the same. 
     
     
       19. The alkenyl aromatic compound-conjugated diene block copolymer according to claim 1, wherein the weight ratio of alkenyl aromatic compound/conjugated diene in said conjugated diene-alkenyl aromatic compound copolymer block is 3-64/97-36.